Fast ein Viertel des Universums besteht aus Dunkler Materie – doch man kann sie weder sehen noch direkt messen. Jetzt wissen Forscher, wo sich ein Teil davon befindet: Eine Karte zeigt erstmals die Verteilung der mysteriösen Masse.
Certain types of supernovae, or exploding stars, are more diverse than previously thought, a University of Arizona-led team of astronomers has discovered. The results, reported in two papers published in the Astrophysical Journal, have implications for big cosmological questions, such as how fast the universe has been expanding since the Big Bang. Most importantly, the findings hint at the possibility that the acceleration of the expansion of the universe might not be quite as fast as textbooks say.
The team, led by UA astronomer Peter A. Milne, discovered that type Ia supernovae, which have been considered so uniform that cosmologists have used them as cosmic “beacons” to plumb the depths of the universe, actually fall into different populations. The findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness.”We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances — and thus when the universe was younger,” said Milne, an associate astronomer with the UA’s Department of Astronomy and Steward Observatory. “There are different populations out there, and they have not been recognized. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn’t appear to be the case.”
The discovery casts new light on the currently accepted view of the universe expanding at a faster and faster rate, pulled apart by a poorly understood force called dark energy. This view is based on observations that resulted in the 2011 Nobel Prize for Physics awarded to three scientists, including UA alumnus Brian P. Schmidt.
Seit Kosmologen in den 1960er Jahren die ersten Spuren des Urknalls nachwiesen, scheint es, als wäre das Universum einem einzigen, unendlich dichten Punkt entsprungen, einer so genannten Singularität. Sollten jedoch die beiden theoretischen Physiker Ahmed Farag Ali und Saurya Das mit ihrem neuen Ansatz richtigliegen, den sie im Fachjournal “Physics Letters B” veröffentlichten, dann gab es diese Singularität nie. Das All hätte schon immer existiert – zumindest in Form einer winzigen, quantenmechanischen Keimzelle.
In ihrer Arbeit mit dem Titel “Cosmology from quantum potential” verwenden der Ägypter und sein indischer Kollege, der in Kanada an der University of Lethbridge lehrt, die so genannte Raychaudhuri-Gleichung. Sie beschreibt, wie sich die Bestandteile des Kosmos bewegen. Die kürzeste Verbindung zwischen zwei Punkten bezeichnet man als Geodäte. Wenn Licht und Teilchen durch das All reisen, sind diese Geodäten gekrümmt – eine Folge der allgemeinen Relativitätstheorie. Verfolgt man diese Bahnen zurück bis zum Urknall, kommt es zur Singularität. Das folgerten die Physiker Stephen Hawking und Roger Penrose bereits Ende der 1960er Jahre aus Einsteins Gleichungen. Seitdem versuchen Kosmologen, diese Situation mit neuen Theorien und mathematischen Tricks loszuwerden. So unvorstellbar die Lage rund um den Urknall ist, sollten zumindest rechnerisch keine unendlich großen und somit unphysikalischen Werte auftreten. Doch gerade das ist bei einer Singularität der Fall.
“A metaphorical chip holding all the programming for our universe stores information like a quantum computer.” This is the radical insight to the foundation of our Universe developed by Mark Van Raamsdonk, a professor of theoretical physics at the University of British Columbia, that says that the world we see around us is a projection from a set of rules written in simpler, lower-dimensional physics—just as the 2D code in a computer’s memory chip creates an entire virtual 3D world.
“What Mark has done is put his finger on a key ingredient of how space-time is emerging: entanglement,” says Gary Horowitz, who studies quantum gravity at the University of California Santa Barbara. Horowitz says this idea has changed how people think about quantum gravity, though it hasn’t yet been universally accepted. “You don’t come across this idea by following other ideas. It requires a strange insight,” Horowitz adds. “He is one of the stars of the younger generation.”
According to MIT’s Alan Guth , originator of the inflationary universe theory, our Universe is a product of eternal inflation –eternal into the future, but not into the past. An eternally inflating Universe produces an infinite number of pocket universes , which in turn are producing more new universes. The old, mature universes are vastly outnumbered by universes that have just barely begun to evolve. Guth called it the “Youngness Paradox.”
Guth says that “the synchronous gauge probability distribution strongly implies that there is no civilization in the visible Universe more advanced than us. We would conclude, therefore, that it is extraordinarily improbable that there is a civilization in our pocket Universe that is at least one second more advanced than we are. Perhaps this argument explains why SETI has not found any signals from alien civilizations.”In Guth’s view, “nature gets a lot of tries — the Universe is an experiment that’s repeated over and over again, each time with slightly different physical laws, or even vastly different physical laws,” says MIT physics professor Robert Jaffe.
Am Südpol hatten Astronomen vermeintliche Spuren von der Entstehung des Universums eingefangen – und deutliche Kritik von Kollegen geerntet. Jetzt verteidigen sie ihre Arbeit – doch es bleiben Unsicherheiten.
What if spacetime were a kind of fluid? This is the question tackled by theoretical physicists working on quantum gravity by creating models attempting to reconcile gravity and quantum mechanics. Some of these models predict that spacetime at the Planck scale (10-33cm) is no longer continuous – as held by classical physics – but discrete in nature. Just like the solids or fluids we come into contact with every day, which can be seen as made up of atoms and molecules when observed at sufficient resolution. A structure of this kind generally implies, at very high energies, violations of Einstein’s special relativity (a integral part of general relativity).
In this theoretical framework, it has been suggested that spacetime should be treated as a fluid. In this sense, general relativity would be the analogue to fluid hydrodynamics, which describes the behaviour of fluids at a macroscopic level but tells us nothing about the atoms/molecules that compose them. Likewise, according to some models, general relativity says nothing about the “atoms” that make up spacetime but describes the dynamics of spacetime as if it were a “classical” object. Spacetime would therefore be a phenomenon “emerging” from more fundamental constituents, just as water is what we perceive of the mass of H2O molecules that form it.Stefano Liberati, professor at the International School for Advanced Studies (SISSA) in Trieste, and Luca Maccione, a research scientist at the Ludwig-Maximilian University in Munich, have devised innovative ways of using the tolls of elementary particle physics and high energy astrophysics to describe the effects that should be observed if spacetime were a fluid. Liberati and Maccione also proposed the first observational tests of these phenomena. Their paper has just been published in the journal Physical Review Letters.
Astrophysicists are casting doubt on what just recently was deemed a breakthrough in confirming how the universe was born: the observation of gravitational waves that apparently rippled through space right after the Big Bang. If proven to be correctly identified, these waves — predicted in Albert Einstein’s theory of relativity — would confirm the rapid and violent growth spurt of the universe in the first fraction of a second marking its existence, 13.8 billion years ago.
The apparent first direct evidence of such so-called cosmic inflation — a theory that the universe expanded by 100 trillion trillion times in barely the blink of an eye — made with the help of a telescope called BICEP2, stationed at the South Pole, was announced in March by experts at the Harvard-Smithsonian Center for Astrophysics. The telescope targeted a specific area known as the “Southern Hole” outside the galaxy where there is little dust or extra galactic material to interfere with what humans could see.”Detecting this signal is one of the most important goals in cosmology today,” John Kovac, leader of the BICEP2 collaboration at the Harvard-Smithsonian Center for Astrophysics, said at the time. By observing the cosmic microwave background, or a faint glow left over from the Big Bang, the scientists said small fluctuations gave them new clues about the conditions in the early universe.
The gravitational waves rippled through the universe 380,000 years after the Big Bang, and these images were captured by the telescope, they claimed. If confirmed by other experts, some said the work could be a contender for the Nobel Prize.But not everyone is convinced of the findings, with skepticism surfacing recently on blogs and scientific US journals such as Science and New Scientist.
Paul Steinhardt, director of Princeton University’s Center for Theoretical Science, addressed the issue in the prestigious British journal Nature in early June. “Serious flaws in the analysis have been revealed that transform the sure detection into no detection,” Steinhardt wrote, citing an independent analysis of the BICEP2 findings.
(hpd) Der amerikanische Physiker Lawrence M. Krauss fasst in seinem Buch den derzeitigen Stand der Forschung im Bereich der Kosmologie in leicht verständlicher Form zusammen. Seine Antwort auf die häufig gestellte Frage in der Form wie sie zuerst der Philosoph Gottfried Wilhelm Leibniz gestellt hat „Warum ist überhaupt etwas und nicht vielmehr nichts?” ist fundiert und klar: „das Nichts ist nicht stabil“.
What caused the matter/antimatter imbalance is one of physics’ great mysteries. It’s not predicted by the Standard Model—the overarching theory that describes the laws of nature and the nature of matter. An international team of physicists has now found the first direct evidence of pear shaped nuclei in exotic atoms. The findings could advance the search for a new fundamental force in nature that could explain why the Big Bang created more matter than antimatter—a pivotal imbalance in the history of everything.
“If equal amounts of matter and antimatter were created at the Big Bang, everything would have annihilated, and there would be no galaxies, stars, planets or people,” said Tim Chupp, a University of Michigan professor of physics and biomedical engineering and co-author of a paper on the work published in the May 9 issue of Nature.
Radical new research is attempting to characterize the properties of a fifth force that disrupts the predictions general relativity makes outside our own galaxy, on cosmic-length scales. University of Pennsylvania astrophysicist Bhuvnesh Jain, says the nature of gravity is the question of a lifetime. As scientists have been able to see farther and deeper into the universe, the laws of gravity have been revealed to be under the influence of an unexplained force.
Two branches of theories have sprung up, each trying to fill its gaps in a different way. One branch — dark energy — suggests that the vacuum of space has an energy associated with it and that energy causes the observed acceleration. The other falls under the umbrella of “scalar-tensor” gravity theories, which effectively posits a fifth force (beyond gravity, electromagnetism and the strong and weak nuclear forces) that alters gravity on cosmologically large scales.
Mit „Ein Universum aus dem Nichts“ fasst der Kosmologe Lawrence Krauss den Stand der momentanen Schöpfungstheorie zusammen – und provoziert nicht nur Kreationisten. Laut Krauss machen die Ergebnisse einen Gottglauben obsolet.
Zuerst leuchtete ein gleißender Funke auf. Aus dem subatomaren Glutball erwuchs in Sekundenbruchteilen ein Gebilde von der Größe einer Pampelmuse, das danach langsam weiter expandierte. Unser All war geboren — hervorgegangen aus dem Feuersturm des Urknalls. Was aber löste diese Urexplosion aus? Stand am Weltenbeginn das Walten eines Gottes, wie es die Schöpfungsgeschichten der Weltreligionen bekunden? Oder brachten natürliche physikalische Prozesse das Universum hervor?
“The fact that heavy elements were plentiful only 5 billion years after the big bang is a very good sign about the possibility of alien-life evolving in the very earlier universe. But of course that then leads to the annoying and now cliche Fermi paradoxical question: If alien life had several billion years to get started earlier than we might have initially expected, then where the heck are they? Consider this: If a hyper intelligent civilization arose when the universe was only 5 billion years old, then it should have had time to effectively colonize every galaxy in the universe, simply by sending out replicating-machines and probes to every visible galaxy at once, simultaneously. And of course once each probe reached the target galaxy, it would only take a few hundred thousands years (or perhaps a couple of million years at most) to establish replicating probes in every star system of that galaxy. So really once life reaches hyper intelligence, then it doesn’t take very long to colonize not only a single galaxy, but the entire universe. Thus there really should be aliens amongst us.
Das Universum ist etwas älter und etwas anders zusammengesetzt als bisher vermutet – doch abgesehen davon scheinen die neuen Ergebnisse des “Planck”-Teleskops kosmologische Standardmodelle zu bestätigen. Wenn da nicht einige unerklärliche Ausnahmen wären.
Ist der Fund des Higgs-Bosons eine schlechte Nachricht für unser Universum? Physik-Theoretiker glauben, dass die Masse des Teilchens in einem Bereich liegt, der dem Kosmos ein Verfallsdatum gibt. Ein baldiges Ende ist jedoch unwahrscheinlich.
“The quantum theory of parallel universes is not the problem, it is the solution. It is not some troublesome, optional interpretation emerging from arcane theoretical considerations,” says David Deutsch. “It is the explanation, the only one that is tenable, of a remarkable and counter-intuitive reality. Everything in our universe — including you and me, every atom and every galaxy — has counterparts in these other universes.”
Legendary Oxford physicist David Deutsch is best known for his contributions to quantum physics, quantum computing, and a leading proponent of the multiverse (or “many worlds”) interpretation of quantum theory — the astounding idea that our universe is constantly spawning countless numbers of worlds.
Could both gravity and the Big Bang be an illusion? In January 2010, Erik Verlinde, professor of Theoretical Physics and world-renowned string theorist, caused a worldwide stir with the publication of On the Origin of Gravity and the Laws of Newton, in which he challenged commonly held perceptions on gravity, going so far as to state ‘for me gravity doesn’t exist’. If he is proved correct, the consequences for our understanding of the universe and its origins in a Big Bang will be far-reaching.
“Everyone who is working on theoretical physics is trying to improve on Einstein,” says Robbert Dijkgraaf, UvA University Professor and current director of the Institute for Advanced Study in Princeton (where scientists including Turing, Oppenheimer and Einstein have worked) In my opinion, Erik Verlinde has found an important key for the next step forward.”
Verlinde, who received the Spinoza prize (the Dutch Nobel Prize) from the Netherlands Organisation for Science, is famous for developing this new theory, or idea, on gravity in which he says that gravity is an illusion. “Gravity is not an illusion in the sense that we know that things fall,” says Verline.” Most people, certainly in physics, think we can describe gravity perfectly adequately using Einstein’s General Relativity. But it now seems that we can also start from a microscopic formulation where there is no gravity to begin with, but you can derive it. This is called ‘emergence’.”